1. Technical Field
This invention relates to amplifiers and, more particularly, to a power combining scheme for combining a plurality of field-effect transistor-based amplifiers.
2. Discussion
In order for millimeter-wave communication systems to be feasible, they generally require high power levels. In the past, the high power requirement had been fulfilled by the traveling wave tubes amplifiers (TWTA). However, the large size, heavy weight and the requirement of extremely high supply voltage for such amplifiers makes it less attractive for space related applications and the like. Currently, the trend has shifted towards using three-terminal solid-state devices such as field-effect transistors (FET), in order to meet the necessary power requirements. These solid-state devices are advantageously smaller, lighter, much more reliable and have low DC power consumption.
In the arena of field-effect transistors, the high electron mobility transistor (HEMT) devices are preferred because of their superior radio frequency (RF) performance in the millimeter-wave frequency range. Currently, however, the available radio frequency power output from a single HEMT amplifier is minimal. Therefore, it is necessary to combine the output power from a plurality of HEMT amplifiers in order to achieve higher power levels. The general scheme of power combining amplifiers in the millimeter-wave frequency range typically includes a radial line for power dividing an input signal amongst the plurality of amplifiers, and a separate radial line for combining the amplified output signals of each amplifier to obtain the output. However, the use of separate power dividing and power combining lines adds to the overall size, weight, cost and complexity of the system.
It is therefore desirable to provide a power combining scheme for combining a plurality of amplifiers which does not require separate radial lines for power dividing and power combining. It is furthermore desirable to provide a single radial line power combiner/divider which eliminates the need for a second radial line to thereby provide a smaller, lighter, more simplified and more cost efficient amplifier system.